Influenza A virus causes serious disease in infants less than six months of age, and thus, there is a need for a vaccine for this age group. 107 TCID50 of a live attenuated cold-adapted influenza A virus vaccine given intranasally at two months of age together with the routine childhood immunizations and repeated at four or six months of age, induced a vigorous immune response in all vaccinees. Thus, it is possible to successfully immunize this young-age group with a cold adapted influenza A virus vaccine. A proposed strategy has been developed for use of live attenuated influenza alone or in conjunction with the licensed non- living vaccine in persons of all ages. The bovine parainfluenza virus type 3 (BPIV3) vaccine, a live virus vaccine designed to protect against the antigenically related human PIV3, was found to be satisfactorily attenuated, stable genetically, poorly transmissible, and immunogenic in seronegative infants and young children older than six months of age. The response of twelve infants less than six months of age to 10/5 TCID50 of virus was similar to that of the 27 older seronegative subjects demonstrating that this vaccine is safe and immunogenic in the young seronegative subject and that it continues to show promise as a vaccine candidate. The live attenuated cold-passaged cp45 human PIV3 vaccine also was found to be satisfactorily attenuated, stable genetically, and immunogenic in seronegative infants and children when administered intranasally at a dose of 10/5 TCID50. A live attenuated intranasal bivalent subgroup A and B RSV vaccine is being developed. A candidate for the subgroup A component is the RSV cpts530/1009 mutant, a cold-passaged, temperature sensitive (cpts) virus. In preliminary Phase 1 studies this candidate vaccine at a dose of 10/4 pfu was found to be attenuated and genetically stable in seronegative infants and young children reproducing similar findings made in chimpanzees. A subgroup B vaccine candidate, designated RSV B1 cpts52/176 was attenuated for adults. Thus, significant progress has been made in the development of a RSV bivalent vaccine.